The subject matter disclosed herein relates to a motion control system with independent carts and a linear drive system. More specifically, the system and method provides ease of operation and automatic adjustment to the speed of travel for the independent carts as they are moved along the linear drive system.
Motion control systems utilizing movers and linear motors can be used in a wide variety of processes (e.g. packaging, manufacturing, and machining) and can provide an advantage over conventional conveyor belt systems with enhanced flexibility, extremely high-speed movement, and mechanical simplicity. The motion control system includes a set of independently controlled carts or “movers” each supported on a track for motion along the track. The track is made up of a number of track segments that, in turn, hold individually controllable electric coils. Successive activation of the coils establishes a moving electromagnetic field that interacts with the movers and causes the mover to travel along the track. Sensors may be spaced at fixed positions along the track and/or on the movers to provide information about the position and speed of the movers.
Each of the movers may be independently moved and positioned along the track in response to the moving electromagnetic field generated by the coils. In a typical system, the track forms a path, which could be a closed path, over which each mover repeatedly travels. At certain positions along the track other actuators may interact with each mover. For example, the mover may be stopped at a loading station at which a first actuator places a product on the mover. The mover may then be moved along a process segment of the track where various other actuators may fill, machine, position, or otherwise interact with the product on the mover. The mover may be programmed to stop at various locations or to move at a controlled speed past each of the other actuators. After the various processes are performed, the mover may pass or stop at an unloading station at which the product is removed from the mover. The mover then completes a cycle along the path by returning to the loading station to receive another unit of the product.
While the mover is travelling along the different segments for filling, machining, placing, returning, and the like or while the mover is travelling along different lengths of track, curves of varying radii, and the like, it may be desirable to command the mover to travel at a different velocity. For example, a curve having a short radius may require the mover to travel at a slower velocity than a curve having a long radius to avoid undesirable centrifugal forces applied to the product on the mover causing damage and/or loss of product. The centrifugal forces applied to the mover may also increase wear on bearings, wheels, and the like. Similarly, it may be desirable to travel at a greater rate of speed along a long straight segment of track when returning an empty mover to a starting position than along a short segment of track when the mover is traveling between stations while loaded with a product.
Historically, it has been necessary for a programmer to generate a sequence of commands for each mover as it travels across each of the different segments. Each command includes a desired velocity and a desired distance for the mover to travel. Further, the programmer must know whether the mover is to stop at the end of travel, continue traveling with an additional move command, and whether the mover is to change velocity or continue at a constant velocity prior to the end of the travel distance. Further, the commands may vary between movers as a function of the loading of the mover. Depending on the configuration of the track, controlling operation of a mover between two positions on the track requires the programmer to generate a series of commands, having five, ten, or even a greater number of commands to control the mover as it travels across the multiple segments of the track between the start position and the end position. Programming movers to travel along the track requires significant knowledge about the configuration of the track, the movers, and the operations being performed along the track and often results in a complex series of commands for each mover to achieve a desired operation of each mover.
Thus, it would be desirable to provide a system and method to simplify programming of the movers.
It is further desirable to provide a system and method that will automatically adapt operation of each mover as it travels along the track.